Ten things more dangerous than sharks

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The great white shark released Mike Fraser only after it had ripped off his arm.

The 53-year-old was attacked in 1992, while snorkelling off Campbell Island 600 kilometres south of Invercargill, surveying the area for photographing and filming southern right whales.

"Suddenly I was hit on the right-hand side like a truck, and I was pulled underwater," Fraser said.

"I saw the shark hanging on to my right arm. The arm came off, which is how I got loose."

As well as using their teeth to test out potential prey, sharks will often injure animals and wait for them to bleed to death before eating them. Fraser suspects this was what the shark was doing to him.

Fortunately, with the help of adrenaline and the cold southern waters that stopped the bleeding, Fraser was able to swim to shore.

Despite the frustrations of losing an arm, Fraser still has great respect for the sharks. He had dived with sharks many times and has worked on documentaries about the predators since the attack.

There are more than 60 shark species that come to New Zealand waters. The majority are little-known species that live deep below the ocean surface.

But New Zealand also attracts the big names that induce fear in the hearts of swimmers.

"Great whites are found throughout New Zealand waters. We get newborns through to mature females, more than five-and-a-half metres long," Department of Conservation shark expert Clinton Duffy said.

But the chances of getting attacked by a shark this summer are very small.

On average, there are two shark attacks every year in New Zealand. Since 1837, there have been 15 fatal attacks. The last death was in 2006, when a kayaker was mauled by a great white in the Coromandel - whether he drowned before the shark found him is still disputed. Before that was 1976.

"Sharks definitely get a bad rep," Duffy said.

Each summer the media is filled with screaming headlines about shark sightings and attacks, but the truth is that - scary though they appear - the giant predators are much less likely to cause us harm than countless other things we humans come across.

Every year about 5000 people die from causes related to smoking. This year, three people had drowned in backyard swimming pools before September. Since 2003, there have been three fatalities by dog attack.

"There are fatal shark attacks and non-fatal injurious shark attacks, but they are very rare events - especially when you consider how many people are in the water every year in this country," Duffy said.

Sharks come to New Zealand to feast in our fertile waters, where they dine on baitfish, kingfish, tuna, marine mammals and other sharks.

But one thing that isn't on a shark's menu is people.

"Fortunately, human beings don't form part of the natural diet," Duffy said.

Fraser suspects the shark spat him out rather than let him go.

But attacks become more likely the closer you are to a seal colony. Great whites gather near seal colonies to hunt and are inquisitive animals. Fraser had been body-surfing with sea lions before he was attacked.

"They are in the general area looking for something about the size of a human being swimming at the surface. Occasionally, they mistake people for seals," Duffy said.

But even in Otago, where seals congregate and the majority of New Zealand's shark attacks have occurred, shark nets that fenced three Dunedin beaches for more than 40 years were removed last year. The nearly $40,000 annual maintenance cost was considered superfluous. In fact, this summer the tables are more likely to be turned on the sharks, which are more likely to be bitten by humans.

Rig sharks and school sharks are an important commercial fishing species in New Zealand and are served in fish and chips.

Before the introduction of the quota management scheme in 1986, their stocks were dangerously depleted.

"There are currently no concerns for the sustainability of those species, but their numbers are clearly down," Duffy said.

The low population of sharks has also made them very difficult to study.

Although very little is known about sharks, research is starting to reveal their importance to the marine ecosystem.

By hunting old, weak and diseased prey, sharks work to keep the ecosystem healthy.

"Sharks are helping to maintain strong species by improving the genetic stock of what is left," said Dr Malcolm Francis, shark researcher at the National Institute of Water and Atmospheric Research. "The prey animals that evolve to avoid predators produce more offspring and increase the genetic pool."

Scientists are becoming increasingly concerned about their vulnerability, primarily to fishing.

Their very low biological productivity makes them susceptible to overfishing. Female sharks reach breeding age at around about half their life expectancy and their gestation period is around 12 months.

"There is no doubt that they are stunningly beautiful animals and we know almost nothing about them," Duffy said.

And what you don't understand, you fear.

Global shark attacks have increased every decade since 1900. Last year's 12 fatalities, three in Australia, was almost three times the average of 4.3 from 2001 to 2010, according to the International Shark Attack File.

In contrast, Greenpeace estimates that 100 million sharks are killed by humans every year.